The present invention relates to a laser diode module, and more specifically to a laser diode module in which the optical axes of a laser diode and an optical fiber pig-tail are each relatively adjusted.
A laser diode (hereinafter referred to as "LD") module used in optical fiber communication is often marketed in the form of a module provided with an optical fiber pig-tail for guiding light output power and is used under an extensive range environmental conditions ranging from low to high temperatures.
FIG. 1 illustrates a longitudinal cross section of a conventional LD module. A laser diode (LD) chip 5 is adjusted in optical axis relative to a ferrule 4 via a lens 2 and the ferrule 4 is fixed to a base 1 via a slide ring 3 by YAG laser welding. An optical fiber 12 is protected at a proximate end by ferrule 4 which is a metal pipe hermetically surrounding the optical fiber 12. The base 1 is fixed to a package or container 9 by soldering, with a Peltier element 11 interleaved therebetween. The ferrule 4 is fixed to the end wall of the package 9 by a solder lib 14 in a manner to be hermetically sealed.
Since the LD module is usually used under environmental conditions that may vary from -20.degree. C. to +70.degree. C., within this range, it is required to retain a stable performance. The conventional package arranged as above expands about 60 .mu.m in the axial direction of the fiber within the atmosphere of +70.degree. C. as compared with a case under the normal temperature (25.degree. C.). This displacement causes mechanical movement of the ferrule 4 fixed by a solder 14. When the ferrule 4 receives such a force, the base 1 would be deformed by being pushed by the ferrule, causing a deviation of the optical axes for the LD chip 5 and the ferrule 4. As a result, the optical output power launched into the optical fiber 12 within the ferrule 4 fluctuates 1 dB or more. This phenomenon will also occur under the environmental condition of -20.degree. C., and yet in the opposite direction, thereby causing a fluctuation of the optical output power. That is, the conventional LD module has a drawback that its optical output power fluctuates by the fluctuation of the environmental temperature.